Sensor device for detection of dissolved hydrocarbon gases in oil filled high-voltage electrical equipment

ABSTRACT

A multi-gas sensor device for the detection of dissolved hydrocarbon gases in oil-filled electrical equipment. The device comprising a semiconductor substrate, one or more catalytic metal gate-electrodes deposited on the surface of the semiconductor substrate operable for sensing various gases, and an ohmic contact deposited on the surface of the semiconductor substrate. The semiconductor substrate comprises one of GaN, SiC, AlN, InN, AlGaN, InGaN and AlInGaN. A method for sensing gas in an oil-filled reservoir of electrical equipment, comprising providing a sensor device, immersing the sensor device in the oil-filled reservoir, allowing the gases emitted from the oil to interact with the one or more catalytic metal gate-electrodes, altering the gas as it contacts the catalytic metal gate-electrodes and altering the sensitivity of the sensor.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to the field of gassensors. More particularly, the present invention relates tosemiconductor gas sensors made from wide bandgap materials such asgallium nitride (GaN) and silicon carbide (SiC) that are effective atproviding continuous or discrete measure of gas levels resulting fromdegradation processes in insulating oil in oil-filled high-voltageelectrical equipment.

[0003] 2. Description of the Related Art

[0004] Gas sensors have been used in the detection of particularsymptomatic gases in oil-filled electrical equipment. Faults inoil-filled transformers, for example, may include arcing (electrical),corona discharge (electrical), low energy sparking (electrical), severeoverloading (electrical), pump motor failure (electrical and thermal)and overheating (electrical and thermal) in an insulation system. Faultsmay generate undesirable gases, such as hydrogen (H₂), acetylene (C₂H₂),ethylene (C₂H₄), methane (CH₄), ethane (C₂H₄), carbon monoxide (CO) andcarbon dioxide (CO₂). These fault conditions result in a malfunctioningtransformer or may indicate an impending malfunction, which, if notcorrected, may lead to failure of the transformer. A statisticalcorrelation exists between transformer malfunction and fault gasesgenerated by the transformer. Accordingly, if the accurate detection ofpotentially dangerous gases in a transformer is achieved, possiblemalfunction and failure of the transformer can be addressed and oftenavoided.

[0005] The principles described previously for oil filled transformersmay also be applied to other pieces of oil filled equipment orfacilities, in which high electrical fields or temperature oscillationscause the oil to break down into its potentially flammable constituentsover time. One example of such equipment includes x-ray tubes used inmedical applications. X-ray tubes supply x-rays used in medicalassessments of bone or tissue structure. These tubes, much liketransformers, use oil to both insulate and cool internal electricalcomponents. Gas sensors fabricated from GaN or SiC would provide anon-intrusive method for maintaining such equipment regularly,minimizing down-time and avoiding catastrophic fault conditions.

[0006] With respect to hydrogen, power transformers expose insulatingoil to high electric fields that break down the oil over time. Hydrogengas and hydrogen bearing compounds are given off, indicating the needfor preventative maintenance. If this need goes unheeded, it may lead tothe build-up of flammable hydrogen gas in the system, which if ignited,may lead to catastrophic failure. Current detection systems for hydrogeninclude oil sampling and chromatographic analysis, single gas sensorsand person-operated units. These conventional approaches are timeconsuming, expensive, offer incomplete information, and in some casesare only performed periodically throughout the year.

[0007] The ability of sensors to identify a target gas depends onseveral factors. These factors include the sensitivity of the sensor toother interfering gases and vapors, and a concentration of the targetgas. The ability to resolve the target gas from other gases is calledthe selectivity. There are very few known sensors that are highlyselective where a sensor has greater than about a tenfold difference ingas detection between sensing states and non-sensing states. Further,within these very few sensors there are even fewer that are relativelyreliable to accurately detect individual gases.

[0008] Current semiconductor gas sensor technology may make use ofSi/SiO₂ as materials on which a gas is sensed. Others may make use ofSnO₂ or other oxides, however, in the case of SnO₂, these devicestypically require a heater to increase their temperature in excess of200 deg C. in order to make them sensitive enough to be useful. Whilethese sensors are mass producible, they often fail in outdoorenvironments where the temperature fluctuates. Temperature fluctuationsmay lead to drift in response to gaseous environments over time, whichmeans that the change in electrical response to the same gas will differover time, thus the sensor system will require temperature correction inorder to track quantitative changes. Even small changes in a temperaturerange, such as about −40 to about 130 deg F., are enough to cause suchdrift over time. Drift is most noticeable in Si devices, making thesedevices ineffective in such ambient settings. In order to minimizedrift, the Si-based sensors often require heating to a temperature of upto about 150 deg C. in order to return the sensors to nominal operatingconditions. Despite the heating, drift over time still occurs due tosurface states formed from oxides and other elements on the surface ofthe sensors.

[0009] U.S. Pat. Nos. 6,041,643, 6,155,100, 6,182,500 and 6,202,473 allissued to Stokes et al., incorporated herein by reference, describe agas sensor for determining the presence of at least one gas in a gaseousenvironment. The gas sensor includes a semiconductor substrate, a thininsulator layer disposed on the semiconductor substrate, a catalyticmetallic gate disposed on the thin insulator layer and a chemicallymodified layer disposed on the catalytic metal gate. The chemicallymodified layer includes a material that protects the sensor fromcorrosive gases and interference from at least one of foreign matter andwater, alters at least one of surface chemical properties and surfacephysical properties of the sensor, and passes only a designated gastherethrough.

[0010] What is needed is a more robust material system for addressingmaterial issues and eliminating drift. What is further needed is a hightemperature, harsh environment capable gas sensor that outperformsconventional solid-state sensors that use semiconductor materials suchas Si.

BRIEF SUMMARY OF THE INVENTION

[0011] In various embodiments, the present invention providessemiconductor gas sensors made from wide bandgap materials such asgallium nitride (GaN) and silicon carbide (SiC) that are effective atproviding a continuous measure of gas levels in oil-filled high-voltageelectrical equipment. These materials are more robust than silicon (Si)and operate well in a wide range of ambient environments. These materialsystems provide chemically stable, repeatable responses in widetemperature ranges and harsh environments and are effective up to about450 deg C. over a wide range of pressures. The term harsh environment ismeant to include temperatures above about 150 deg C., where Si devicesdegrade and suffer significant reliability issues. Harsh environmentsmay also include high pressures, high vibrations, a combination thereinor other.

[0012] In one embodiment, the present invention provides a multi-gassensor device comprising a semiconductor substrate, one or morecatalytic metal gate-electrodes deposited on the surface of thesemiconductor substrate, and an ohmic contact deposited on the surfaceof the semiconductor substrate. Each catalytic metal-gate electrode maybe operable for sensing a different gas. The multi-gas sensor deviceoperates in a gaseous environment, such as immersed in electricallynon-conductive oil containing dissolved gases.

[0013] In another embodiment, the semiconductor substrate is selectedfrom the group consisting of group III, IV and V materials, such as GaN,SiC, AlN, AlGaN, InN, InGaN and AlInGaN. The one or more catalytic metalgate-electrodes comprise platinum, palladium, iridium, ruthenium,nickel, copper, rhodium, molybdenum, iron, cobalt, titanium, vanadium,tantalum, tungsten, chromium, manganese, gold, silver, aluminum,palladium:silver, tin, osmium, magnesium, zinc, alloys of thesematerials and combinations of these materials.

[0014] In a further embodiment, the gases comprise hydrogen,hydrogen-bearing, oxygen, oxygen-bearing and others, and are a result ofthe degradation of oil caused by heat and electric fields.

[0015] In a still further embodiment, the present invention provides agas sensor device comprising a semiconductor substrate, a catalyticmetal gate-electrode deposited on the semiconductor substrate, an ohmiccontact deposited on the semiconductor substrate, a passivation layeroperable for increasing the selectivity of the device to a gas and aheating mechanism. The passivation layer may comprise silicon nitride,silicon dioxide, silioxynitride, hafnium oxide, titanium oxide, indiumdoped titanium oxide, aluminum oxide, gallium oxide, or alloys orcombinations of these materials.

[0016] In a still further embodiment, a method is provided for detectingvarious gases. The method comprises providing a sensor device, immersingthe sensor device in an oil-filled environment, allowing the oil-filledenvironment to interact with the one or more catalytic metalgate-electrodes, altering the various gases as they contact thecatalytic metal gate-electrodes, the altering comprising at least one ofatomically and molecularly altering chemical structure of the variousgases, and altering the sensitivity of the sensor device. The sensordevice comprises a semiconductor substrate, one or more catalytic metalgate-electrodes deposited on the surface of the semiconductor substrate,wherein each of the one or more catalytic metal gate-electrodes isoperable for sensing a different gas, and an ohmic contact deposited onthe surface of the semiconductor substrate.

[0017] In a still further embodiment, a method for sensing various gasescomprises providing a sensor device, immersing the sensor device in theoil-filled reservoir, allowing the oil to interact with the one or morecatalytic metal gate-electrodes, altering the gas as it contacts thecatalytic metal gate-electrodes, the altering comprising at least one ofatomically and molecularly altering chemical structure of the gas, andaltering the sensitivity of the sensor device. The sensor devicecomprises a semiconductor substrate, one or more catalytic metalgate-electrodes deposited on the surface of the semiconductor substrate,an ohmic contact deposited on the surface of the semiconductorsubstrate, a passivation layer operable for increasing the selectivityof the device to the gas and a heating mechanism for increasing thesensor device response to the gases.

[0018] In a still further embodiment, a method for sensing various gasescomprises providing a sensor device, immersing the sensor device in theoil-filled reservoir, allowing only the gases in the oil to interactwith the one or more catalytic metal gate-electrodes by using aprotective, selectively porous membrane material, altering the gas as itcontacts the catalytic metal gate-electrodes, the altering comprising atleast one of atomically and molecularly altering chemical structure ofthe gas, and altering the sensitivity of the sensor device. The sensordevice comprises a semiconductor substrate, one or more catalytic metalgate-electrodes deposited on the surface of the semiconductor substrate,an ohmic contact deposited on the surface of the semiconductorsubstrate, a passivation layer operable for increasing the selectivityof the device to the gas, a heating mechanism for increasing the sensordevice response to the gases, and a protective gate material such as aselectively porous membrane which allows only certain gases to passthrough it to the semiconductor device and its catalytic metals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] A variety of specific embodiments of this invention will now beillustrated with reference to the Figures. In these Figures, likeelements have been given like numerals.

[0020]FIG. 1 is a schematic diagram illustrating a multi-gas sensordevice comprising three gate-electrodes in accordance with an exemplaryembodiment of the present invention;

[0021]FIG. 2 is a schematic diagram illustrating a gas sensor devicecomprising one Schottky contact in accordance with an exemplaryembodiment of the present invention;

[0022]FIG. 3 is an illustration of packaging for the multi-gas sensordevice of FIG. 1 in accordance with an exemplary embodiment of thepresent invention;

[0023]FIG. 4 is an illustration of packaging for the multi-gas sensordevice of FIG. 3 further comprising a protective gate or membranematerial in accordance with an exemplary embodiment of the presentinvention;

[0024]FIG. 5 is a graph illustrating current vs. voltage characteristicsof the multi-gas sensor device of FIG. I in accordance with an exemplaryembodiment of the present invention; and

[0025]FIG. 6 is a graph illustrating the response to variousconcentrations of hydrogen as a function of time in accordance with anexemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0026] As required, detailed embodiments of the present invention aredisclosed herein, however, it is to be understood that the disclosedembodiments are merely exemplary of the invention that may be embodiedin various and alternative forms. Specific structural and functionaldetails disclosed herein are not to be interpreted as limiting, butmerely as a basis for the claims as a representative basis for teachingone skilled in the art to variously employ the present invention.Throughout the drawings, like elements are given like numerals. Thesystems described below apply to sensing levels of gases in insulatingoil in oil-filled high-voltage electrical equipment, however, inprinciple also apply to any system that benefits from gas sensing.

[0027] The present invention will now be described with a sensoroperating in electrically non-conductive oil, such as in powertransformer or x-ray tube oil reservoirs, which are merely exampleapplications for the sensor. The sensor may also operate in air and formpart of an exhaust gas monitoring system for gas turbines, diesellocomotives and aircraft engines, where the detection of gases isdesirable. The sensor, its operation and the detection of hydrogen gasare merely exemplary and are not meant to limit the invention.

[0028] Referring now to FIG. 1, a gas sensor device 10 for gas-in-oildetection in high power electrical equipment/transformers isschematically shown. The sensor device 10 may make use of an inducedelectrical field at the surface of the device 10 from hydrogen ions,and/or hydrogen molecules that are polarized. The polarization may bedetected by measuring current-voltage characteristics, or by measuringthe capacitance of the device 10. This may be accomplished using severalconfigurations such as a diode (Schottky) with a catalyticgate-electrode, a capacitor or a field effect transistor (FET) ofdifferent configurations, which use a catalytic metal as the gate.

[0029] The gas sensor device 10 comprises a multi-electrode gas sensorfabricated on a semiconductor layer 12. The semiconductor layer 12 isepitaxially grown over a substrate layer 14. The substrate layer 14comprises an inorganic crystallization growth substrate, such assapphire, silicon, silicon carbide, aluminum oxide, aluminum nitride,gallium nitride, gallium arsenide, aluminum gallium nitride, lithiumgallate or any other substrate capable of supporting crystal growth onat least a portion of exposed area of the surface of the substrate 14.

[0030] The device 10 comprises several electrode metals, each having adifferent sensitivity to different gases, making it a multi-gas sensor.Each electrode response is proportional to the concentration of a targetgas, and the response to the target gas is high enough to overcomebackground noise. In one embodiment, the present invention comprises atwo or more terminal solid-state gas sensor device fabricated from agroup-III/IV/V-based semiconductor epitaxial layer 12 onto which thinmetal catalytic gate-electrodes 16, 18, 20 (e.g., Schottky contacts) aredeposited. FIG. 1 shows three gate-electrodes for exemplary purposes,however, the sensor device 10 of the present invention may be practicedusing two or more gate-electrodes incorporated into a single largedevice, however, an array of different devices is also envisioned.Etching may be used to isolate gate-electrode components. A potentialchange of the gate-electrode 16, 18, 20 leads to a change in theelectronic equilibrium in the underlying n- or p-type semiconductorlayer 12. The sensor device further comprises a thick metallic ohmiccontact 22 deposited on the semiconductor layer 12.

[0031] The gate-electrodes 16, 18, 20 serve as catalysts for apolarization layer from a set of gases (hydrogen, hydrogen bearing,oxygen, oxygen bearing, among others). The metallic gate-electrodes 16,18, 20 comprise a suitably thick layer of material of an appropriatecorrosive-resistant gate material. For example, the materials of themetallic gate-electrodes 16, 18, 20 comprise an appropriate metallicmaterial, such as, but not limited to at least one of: platinum,palladium, iridium, ruthenium, nickel, copper, rhodium, molybdenum,iron, cobalt, titanium, vanadium, tantalum, tungsten, chromium,manganese, gold, silver, aluminum, palladium:silver, tin, osmium,magnesium, zinc, alloys of these materials, and combinations of thesematerials.

[0032] The different catalytic metals possess different sensitivities tovarious gases of interest, making the single sensor device 10 operablefor detecting several gaseous elements, distinguishing between them anddetermining concentrations. The catalytic gate-electrodes 16, 18, 20have a thickness in a range preferably between about 5 nm to about 100nm, more preferably from about 8 nm to about 50 nm, and even morepreferably about 20 nm in thickness. The thickness of the metallicgate-electrodes 16, 18, 20 depend on the intended use of the sensordevice 10. The level of sensitivity for each gas may be different foreach particular gate material. The sensor device 10 may be tuned to aparticular gas by virtue of the particular gate material chosen, and/orby modifying the surface geometry and/or area in which each particularmetal is placed.

[0033] For high temperature applications, the gas sensor device 10 maybe made up of semiconductor materials from group-III, IV and Vmaterials. The most common alloys that may be used in the practice ofthe present invention comprise binary alloys such as GaN, InN, SiC andAlN. Ternary alloys, such as AlGaN and InGaN, and quaternary alloys,such as AlInGaN, may also be considered for use in the presentinvention. These alloys, such as GaN and SiC, are both resistant toharsh environments and capable of operation at high temperatures, suchas over about 150 deg C. In addition, the chemical inertness of GaN andSiC gives them a high resistance to etching and degradation, even in thepresence of strong acids or bases. The wide bandgaps of GaN and SiC makethese materials ideal for the harsh environments described above.Different semiconductor materials may be combined to achieve differingresponses and sensitivities in arrays or single devices.

[0034] The sensor device 10 provides for the continuous, accurate andrepeatable detection of potentially hazardous gases in an ambientenvironment ranging from about −40 to about 130 deg F. without sensordrift, which is a common problem in currently used Si sensor technology.Different temperatures may be used with various diodes or on an array orsingle diode for temperature dependent variance in sensitivity todifferent gases.

[0035] A low-resistance ohmic contact 22 is necessary in the successfulimplementation of the multi-gas sensor device 10. For example, a Ti/Al(300/710 Å) or Ti/Pt/Au (200/200/2600 Å) layers may be deposited viaconventional electron beam evaporation onto a GaN substrate and then maybe thermally annealed at an appropriate temperature and time (about 900deg C. for about 30 sec.) using a rapid thermal annealing technique.

[0036] Initially, hydrogen gas molecules (H₂) are adsorbed onto ametallic gate-electrode from the surrounding ambient environment. Theadsorbed molecules are altered, such as by being catalyticallydissociated from each other on a molecular or atomic level. For hydrogengas (H₂), the molecules (H₂) are dissociated into individual hydrogenatoms (H). Next, the atomic hydrogen (H) diffuses through the metallicgate-electrode to the interface at the semiconductor surface 12. Thediffusion forms a dipole layer that electrically alters the Schottkybarrier (height) of the Schottky/GaN interface. In one embodiment, thebarrier height may be monitored electrically such as by applying aconstant voltage or bias through the diode while monitoring the currentacross the diode. In another embodiment, the barrier height may bemonitored by maintaining a constant current through the diode andobserving as a change in voltage. The magnitude of change in theSchottky barrier height increases as a gas concentration increases, andmay thereby be used to determine gas concentration quantitatively. Manyindividual gases containing hydrogen, such as, but not limited to,amines, mercaptans, hydrocarbons, and alcohols, may be detected in thismanner by the sensor device 10.

[0037] GaN and SiC gas sensor devices 10 avoid the development ofsurface states due to the very slow nature of their oxidation processes,thereby increasing their response stability over time. This makes thesesemiconductor materials ideal for the continuous monitoring ofconcentrations of hydrogen or hydrogen-bearing compounds, and/or oxygenor oxygen-bearing compounds. Additionally, by using various metals forthe gate-electrodes 16, 18, 20, the sensitivity to a combination ofgases is also possible, thereby providing for the real time monitoringof a complex environment, such as a transformer oil reservoir.

[0038] Referring now to FIG. 2, an additional schematic diagram andcross-section of the sensor device 10 is illustrated. The sensor device10 makes use of at least one gate-electrode (Schottky contact) 16 andone ohmic contact 22. A bond metal 23 serves to make electrical contactfrom a wire to the catalytic metal 16, or Schottky contact 16. As statedabove, the semiconductor layer 12 may be any n-type, p-type orintrinsically doped GaN, AlN, AlGaN, AlInGaN, or SiC. The semiconductorlayer 12 may be within a range of about 500 nm to several microns inthickness and is grown on a substrate 14. The sensor device 10 comprisesat least one metal electrode (Ti for n-type, Pt for p-type and Al forboth if so desired) for ohmic contact to the device for monitoring theelectrical properties of the sensor device 10. The geometry of thesensor device 10 is such that the gate-electrode 16 and ohmic contact 22are disposed in close proximity for increased sensitivity, preferablywithin about 2 microns to about 1 mm. An oxide passivation layer 24 maybe applied to the surface of the sensor device 10 to passivate anydangling bonds at the surface and reduce leakage currents. The sensordevice 10 may comprise a cover layer or may be disposed in a spacebehind a membrane, where the cover layer or membrane serve forprotection or gas filtering to modify the concentration of reactantgases. An array of sensor devices 10 may be used, each with a differentcover layer or membrane that responds in a different manner to adifferent gas.

[0039] Referring now to FIG. 3, an illustration of the packaging of thesensor device 10 is shown. A packaging body 26 houses the sensor device10, semiconductor layer 12 and heating element resistors disposed aroundthe device 10 on the epilayer, or underneath the semiconductor chip 30.The heating element resistors may be used for generating faster responsetimes, with the addition of heat to the surface of the sensor. Here,dissociated gas species that cause a response, are provided with thermalenergy via the heating. This decreases their residency time on thesurface, and thus a faster response from the sensor. In anotherembodiment, the sensor device 10 itself may be the heating elementwhereby a large current is passed through the device 10 in order to heatit to a temperature of about 150 deg C. Optionally, other heatingelements such as a metal layer disposed underneath the sensor device 10or a thermoelectric heater 30 disposed either underneath or on the sideof the sensor device 10 may be used. The GaN or SiC materials used forthe semiconductor layer 12 are able to withstand temperatures over about450 deg C. without experiencing degradation. The operation of the sensordevice 10 at temperatures of about 200 deg C. and above generallyresults in faster responses (sensitivity) to various gases.

[0040] Referring now to FIG. 4, an illustration of the sensor packagingmay comprise a header and lid assembly 40. The header and lid assembly40 may be soldered, resistance welded, or epoxied to facilitate ahermetic seal. A hole may then be drilled through the lid and a thinfilm 42 may be applied across the assembly 40 to permit the passage ofonly specifically chosen atoms or molecules to the surface of the sensordevice 10. In one embodiment, Teflon may be held in the lid mechanicallyusing pins or other fastening mechanisms. In another embodiment, Kaptonmay be epoxied around sealed edges of the lid. In yet anotherembodiment, a film of diamond like carbon may be deposited on the lid ofthe package to provide a corrosion-resistant hermetic seal. Packagingtechniques in which arrays of sensor devices comprise different membranematerials provide for selectivity among various gases.

[0041] Referring now to FIG. 5, the current-voltage (I-V)characteristics of the gas sensor device 10 are shown in a logarithmicplot. Here, the device behavior indicates that in reverse bias, theleakage current is approximately 1 microamp at negative 10 volts, whilein forward bias, the current quickly attains levels in the milliamps orhigher. The most important feature of this figure is the sharp increasein current from approximately 0 to 1 volt. As the device may be operatedin or near this voltage range, the sharper the increase, the higher thesensitivity the sensor will have to gases.

[0042] Referring now to FIG. 6, the responses (current) of the gassensor device 10 to various concentrations of hydrogen as a function oftime are shown. FIG. 5 highlights the strong response of the sensordevice 10 to hydrogen as operated. This data also shows that once thegas concentrations are lowered (e.g. from 1% H₂ to 0.1% H₂), the currentin the device follows that trend. Although this figure illustrates theresponse of a gas sensing diode operated in the constant voltage mode,it may also be operated in the constant current mode. In this case, adesignated current level is applied to the diode, and the resultingvoltage is measured. This method also has the advantage that as thecurrent is held constant throughout the measurement, so is the internal(resistive) heating level. Thus, the epitaxial layers (and surface) seethe same heating during the range of gases exposed, which is converse tothe constant-voltage method of measurement.

[0043] In the FET type device of the present invention, the FETstructure is a natural amplifier, i.e. a small change in the Schottkypotential may cause large changes in the channel current, which makesthe sensor device 10 more sensitive. By using a silcon nitride (Si₃N₄)passivation layer, the sensor device may mitigate effects of surfacestates that may potentially cause false signals due to an interaction ofthe surface states with positive ions other than hydrogen. The Si₃N₄layer thereby increases the selectivity to hydrogen as the hydrogeninteracts with the semiconductor layer by diffusing through the metallicgate, whereas the other large molecules are prevented from interactingwith the surface. Further improvements to sensitivity may beaccomplished by adding a Teflon or Kapton cover to the sensor device 10.Some variations of Teflon material has a selectivity of about 10:1 forH₂:O₂ or greater, which provides increased sensitivity. Kapton'sselective porosity is even greater, near 20:1. The Teflon or kaptoncover may be used to filter gas compounds from a main cell in anextraction cell for increased gas concentrations.

[0044] There are several methods for which measurement data may beextracted from the described sensor embodiments. These include measuringa sensor's electrical current while applying a constant voltage, ormeasuring a voltage while applying a constant current. Additionally, thecapacitance of a device may also be measured, as the capacitance ismodified with gas concentration. All of these methods or combinations ofthem may be applied to a single, two electrode device such as a diode,capacitor, or a three electrode transistor. These or other methods alsoexist for extracting a simultaneous measurement of two or more gases,using the same types, or extensions of these device configurations.

[0045] To facilitate the measurement of two or more gases, an array ofindividual devices or a larger device incorporating multiple featuresmay be used. These multiple features may include a large fingered deviceas shown in FIG. 1, whereby finger 16 is comprised of one catalyticmetal, finger 18 is comprised of a second and finger 20 is comprised ofa third and so on. As different catalytic metals have differingcatalysis mechanisms to many gases, these may be taken advantage of inthe simultaneous sensing of more than one gas species (e.g. ethylene,methane and hydrogen) to form a multi gas sensor.

[0046] In another embodiment of a multi gas sensor, one may modify thetemperature of individual devices separately, or individual sections ofa larger device. For example, individual heating (or cooling) elementsmay be used to separately and differently heat finger 16, from finger 18from finger 20. A modification in the temperature of the surface of afinger will cause a modification in the desorption rate of reacted gasspecies from the surface. By measuring the rate at which each separatelyheated (or cooled) section or finger turns on or off may describe thegas species present. Additionally, fingers 16, 18 and 20 may becomprised of different catalytic metals that have varying responses todifferent gases. An algorithm may be then applied to extract informationabout separate gases.

[0047] It is apparent that there have been provided, in accordance withthe device and methods of the present invention, a sensor device forgas-in-oil detection. Although the device of the present invention hasbeen described with reference to preferred embodiments and examplesthereof, other embodiments and examples may perform similar functionsand/or achieve similar results. All such equivalent embodiments andexamples are within the spirit and scope of the present invention andare intended to be covered by the following claims.

What is claimed is:
 1. A gas sensor device, comprising: a semiconductorsubstrate; one or more catalytic metal gate-electrodes deposited on thesurface of the semiconductor substrate; and an ohmic contact depositedon the surface of the semiconductor substrate; wherein the catalyticmetal-gate electrode is operable for sensing a gas; and wherein themulti-gas sensor device operates immersed in electrically non-conductiveoil.
 2. The device of claim 1, wherein the semiconductor substrate isselected from the group consisting of group III, group IV and group Vmaterials.
 3. The device of claim 2, wherein the semiconductor substrateis selected from the group consisting of GaN, SiC, AlN, InN, AlGaN,InGaN and AlInGaN.
 4. The device of claim 1, wherein the one or morecatalytic metal gate-electrodes are selected from the group consistingof platinum, palladium, iridium, ruthenium, nickel, copper, rhodium,molybdenum, iron, cobalt, titanium, vanadium, tantalum, tungsten,chromium, manganese, gold, silver, aluminum, palladium:silver, tin,osmium, magnesium, zinc, alloys of these materials and combinations ofthese materials.
 5. The device of claim 1, wherein the one or morecatalytic metal gate-electrodes comprise a Schottky contact.
 6. Thedevice of claim 1, wherein the gases sensed are selected from the groupconsisting of hydrogen, hydrogen bearing gases, oxygen andoxygen-bearing gases.
 7. The device of claim 1, wherein the device isoperable for the detection of hydrocarbon gases dissolved in transformeroil.
 8. The device of claim 1, wherein the device is operable for thedetection of gas-in-oil in x-ray tubes.
 9. The device of claim 1,wherein the device is operable in an ambient environment ranging fromabout −40 deg C. to about 450 deg C.
 10. The device of claim 1, furthercomprising a coating operable for protection and gas filtering in orderto modify the concentration of the gases.
 11. The device of claim 10,wherein the coating may be comprised of fluorocarbon resins, polymers ofpolytetrafluoroethylene, diamond like carbon or a combination of thosefilms.
 12. The device of claim 1, further comprising heating elementresistors disposed adjacent to the device.
 13. The device of claim 1,wherein the sensor device itself is a heating element whereby a currentis passed through the device in order to heat the device to atemperature up to about 300 deg C.
 14. The device of claim 1, whereinthe device is selected from the group consisting of a diode structure, acapacitor and a field effect transistor.
 15. A gas sensor device,comprising: a semiconductor substrate; a catalytic metal gate-electrodedeposited on the semiconductor substrate; an ohmic contact deposited onthe semiconductor substrate; a passivation layer; and a heatingmechanism; wherein the passivation layer increases the selectivity ofthe device to a gas.
 16. The device of claim 15, wherein the passivationlayer comprises silicon nitride, silicon dioxide or indium tin oxide.17. The device of claim 15, wherein the semiconductor substrate isselected from the group consisting of group III, group IV and group Vmaterials.
 18. The device of claim 17, wherein the semiconductorsubstrate is selected from the group consisting of GaN, SiC, AlN, InN,AlGaN, InGaN and AlInGaN.
 19. The device of claim 15, wherein thecatalytic metal gate-electrode is selected from the group consisting ofplatinum, palladium, iridium, ruthenium, nickel, copper, rhodium,molybdenum, iron, cobalt, titanium, vanadium, tantalum, tungsten,chromium, manganese, gold, silver, aluminum, palladium:silver, tin,osmium, magnesium, zinc, alloys of these materials and combinations ofthese materials.
 20. The device of claim 15, wherein the device isoperable for the detection of dissolved hydrocarbon gases in transformeroil.
 21. The device of claim 15, wherein the device is operable for thedetection of gas-in-oil in x-ray tubes.
 22. The device of claim 15,wherein the gas sensed is selected from the group consisting ofhydrogen, hydrogen-bearing gases, oxygen and oxygen-bearing gas.
 23. Thedevice of claim 15, further comprising a coating operable for protectionand gas filtering in order to modify the concentration of the gas. 24.The device of claim 15, wherein the heating mechanism is selected fromthe group consisting of a heating resistor, a heating layer and athermoelectric heater.
 25. A method for sensing various gases,comprising: providing a sensor device, the sensor device comprising: asemiconductor substrate; one or more catalytic metal gate-electrodesdeposited on the surface of the semiconductor substrate, wherein each ofthe one or more catalytic metal gate-electrodes is operable for sensinga different gas; and an ohmic contact deposited on the surface of thesemiconductor substrate; immersing the sensor device in an oil-filledenvironment; allowing the oil-filled environment to interact with theone or more catalytic metal gate-electrodes; altering the various gasesas they contact the catalytic metal gate-electrodes, the alteringcomprising at least one of atomically and molecularly altering chemicalstructure of the various gases; and altering the response of the sensordevice.
 26. The method of claim 25, further comprising selecting thesemiconductor substrate from the group consisting of GaN, SiC, AlN, InN,AlGaN, InGaN and AlInGaN.
 27. The method of claim 25, further comprisingselecting the catalytic metal gate-electrode from the group consistingof platinum, palladium, iridium, ruthenium, nickel, copper, rhodium,molybdenum, iron, cobalt, titanium, vanadium, tantalum, tungsten,chromium, manganese, gold, silver, aluminum, palladium:silver, tin,osmium, magnesium, zinc, alloys of these materials and combinations ofthese materials.
 28. The method of claim 25, wherein the gases sensedare selected from the group consisting of hydrogen, hydrogen-bearinggases, oxygen and oxygen-bearing gases.
 29. The method of claim 25,wherein the method is used in the detection of dissolved hydrocarbongases in transformer oil.
 30. The method of claim 25, wherein the sensordevice is operable for the detection of gas-in-oil in x-ray tubes. 31.The method of claim 25, wherein the sensor device is operable in anambient environment ranging from about −40 deg C. to about 450 deg C.32. The method of claim 25, wherein the sensor device further comprisesa coating operable for protection and gas filtering in order to modifythe concentration of the gases.
 33. The method of claim 25, wherein thecoating may be comprised of fluorocarbon resins, polymers ofpolytetrafluoroethylene, diamond like carbon or a combination of thosefilms.
 34. A method for sensing gas in an oil-filled reservoir ofelectrical equipment, comprising: providing a sensor device, the sensordevice comprising: a semiconductor substrate; one or more catalyticmetal gate-electrodes deposited on the surface of the semiconductorsubstrate, wherein each of the one or more catalytic metalgate-electrodes is operable for sensing a different gas; an ohmiccontact deposited on the surface of the semiconductor substrate; apassivation layer operable for increasing the selectivity of the deviceto the gas; and a heating mechanism; immersing the sensor device in theoil-filled reservoir; allowing the oil to interact with the one or morecatalytic metal gate-electrodes; altering the gas as it contacts thecatalytic metal gate-electrodes, the altering comprising at least one ofatomically and molecularly altering chemical structure of the gas; andaltering the response of the sensor device.
 35. The method of claim 34,wherein the sensor device further comprises a coating operable forprotection and gas filtering in order to modify the concentration of thegas.
 36. A method for sensing gas in an oil-filled reservoir ofelectrical equipment, comprising: providing a sensor device, the sensordevice comprising: a semiconductor substrate; one or more catalyticmetal gate-electrodes deposited on the surface of the semiconductorsubstrate, wherein each of the one or more catalytic metalgate-electrodes is operable for sensing a different gas; an ohmiccontact deposited on the surface of the semiconductor substrate; apassivation layer operable for increasing the selectivity of the deviceto the gas; a protective gate material which is porous to selectedgases, and a heating element; immersing the sensor device in theoil-filled reservoir; allowing the selectively porous membrane materialto allow only oil emitted gases to interact with the sensor; alteringthe gas as it contacts the catalytic metal gate-electrodes, the alteringcomprising at least one of atomically and molecularly altering chemicalstructure of the gas; and altering the response of the sensor device.